units of variable 'Dwave'

Discussion of how to use ROMS on different regional and basin scale applications.

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lcbernardo
Posts: 59
Joined: Wed Oct 01, 2014 8:57 pm
Location: Tokyo Institute of Technology

units of variable 'Dwave'

#1 Post by lcbernardo » Fri Feb 01, 2019 6:08 am

Hi! Lately I have been coupling ROMS with SWAN and have selected some of the wave parameters for output and I'm confused about the units for Dwave, defined as the 'wind-induced wave direction'. It says 'degrees' (but it also has [radians] next to it, which is also confusing) in varinfo.dat, but is this with respect to North, or the positive x-axis? And does it indicate the direction to or from? I apologize for the simple nature of this question. In my SWAN setup, I have been following the Cartesian convention.

Lawrence

jcwarner
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Location: USGS, USA

Re: units of variable 'Dwave'

#2 Post by jcwarner » Fri Feb 01, 2019 12:49 pm

Lawrence-
if you are using roms + swan, i recommend that you use COAWST instead, we have been updating swan there, adding new wave physics, etc. You can send me an email at jcwarner@usgs.gov to get that code.
In short, Dwave output is in degrees, direction that the waves are from. (because we set NAUTICAL in the swan.in)

lcbernardo
Posts: 59
Joined: Wed Oct 01, 2014 8:57 pm
Location: Tokyo Institute of Technology

Re: units of variable 'Dwave'

#3 Post by lcbernardo » Sat Feb 02, 2019 6:30 am

Hi John, thank you for your reply. Actually I already sent you an email before and have already been using the COAWST system. So this question actually refers to the COAWST framework, even as I continue to use Rutgers ROMS for other applications.

In my swan.in, I have been using CARTESIAN instead of NAUTICAL. So does it follow then that the DWave in my ROMS history file also follows the Cartesian convention (clockwise positive with respect to the positive x-axis, and showing where the waves are going to)?

Thanks,
Lawrence

jcwarner
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Location: USGS, USA

Re: units of variable 'Dwave'

#4 Post by jcwarner » Sat Feb 02, 2019 3:38 pm

Well, for some reason SWAN uses the word 'Cartesian' for 2 separate things.

SET NAUTICAL = winds/waves dir from
or
SET CARTESIAN = winds/waves dir towards

and now for something completely different

COORDINATES CARTESIAN = uses x-y in meters
or
COORDINATES SPHERICAL = uses lat + lon

more info in the swan manual.

lcbernardo
Posts: 59
Joined: Wed Oct 01, 2014 8:57 pm
Location: Tokyo Institute of Technology

Re: units of variable 'Dwave'

#5 Post by lcbernardo » Mon Feb 04, 2019 3:49 am

The first few lines of my swan.in input file are:

MODE NONSTATIONARY TWODIMENSIONAL

SET DEPMIN 0.10 INRHOG CARTESIAN
COORDINATES SPHERICAL

Also, later in the file, I use BOUNDSPEC to define boundary segments, and use CONSTANT FILE to specify time series wave data. And in the data file, I provided the wave direction in the Cartesian convention, which I believe to be consistent with my SET statement. I guess my confusion is that from my SWAN configuration, the wave direction convention appears to be Cartesian, but when the 'Dwave' data is written by ROMS to the history file, will the convention be consistent with SWAN, or will it be converted to nautical?

chegermiller
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Location: University of California at Santa Cruz

Re: units of variable 'Dwave'

#6 Post by chegermiller » Mon Feb 04, 2019 4:01 pm

Hi Lawrence,

We don't currently have a rotation dependent on whether the user chooses Cartesian or Nautical (in SET) in the coupling scripts for ROMS and SWAN. So, the convention is consistent with your SWAN input right now. We recommend that you swap everything to Nautical though because that is what is assumed for the wave-current interaction formulations. We will work on putting a check in so there's no confusion.

Christie

lcbernardo
Posts: 59
Joined: Wed Oct 01, 2014 8:57 pm
Location: Tokyo Institute of Technology

Re: units of variable 'Dwave'

#7 Post by lcbernardo » Tue Feb 05, 2019 5:48 am

Thank you for your reply Christie! I appreciate the short explanation. I'll also try to use the Nautical convention instead for my runs as you recommended.

Lawrence

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